ITR: Improving the Security of Quantum Cryptography with Modified Coherent State

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Intellectual MeritProgress has been made in producing single photon states. But so far those sources havesmall efficiency and are wavelength dependent and are limited for practical applications.Recently a new scheme was proposed and demonstrated for producing photon sourcewith sub-Poissonian photon statistics. The scheme relies on a two-photon quantuminterference phenomenon to reduce and eventually cancel the two-photon events from acoherent state. In this program, we propose to implement the scheme in an opticalcommunication environment. More specifically, we will start with a fiber pulsed laser asthe primary source and use a combination of wave guide nonlinear optical materials toproduce a two-photon state for canceling the two-photon events in a coherent state. Thetechnical challenge will primarily be the temporal mode match for a complete destructivetwo-photon interference. Such a source has the advantages of high secure data rate,well-defined direction and wavelength independence for practical application inquantum cryptography. This source can also be used to form a three-photon interferometer fornonlocality test of quantum mechanics.Broader ImpactsQuantum cryptography, when implemented in the correct condition, will provideunbreakable codes for secure communication. The potential benefit of this technology istremendous, given the current status of security issue in information technology. Theproposed program will significantly improve the applicability of quantum cryptography.Participation of graduate students and undergraduate students in the research is anintegral part of the proposed program, which will train and prepare next generationquantum physicists for the information age in the new century. Results of the researchwill be published in international journals to enhance scientific and technologicalunderstanding.